Vertebrate muscle Z-line structure: an electron microscopic study of negatively-stained myofibrils.

Structural features of the Z-lines of rabbit psoas muscle myofibrils have been studied in the electron microscope with a negative staining technique. The results obtained suggest the presence of about 20 nm periodicity in the structural organization of the Z-line region: a band pattern of five bands of extra density spaced about 20 nm apart was revealed in the Z-region and the Z-filaments connecting actin filaments from neighbouring sarcomeres often appeared to be positioned at intervals of 17-20 nm. An electron microscopic investigation of the interaction in vitro of two major Z-line proteins, alpha-actinin and F-actin, indicated that the positions of alpha-actinin bridges between actin filaments are defined by relative azimuthal positions of actin subunits. A possible arrangement of actin-linking macromolecular bridges in the Z-region is considered. It is supposed that the arrangement of the Z-filaments is related to the helical symmetry of actin-containing filaments. Also, the banded appearance of the Z-region is interpreted as arising from the arrangement of crossbridges connecting thin filaments of the same sarcomeres.

The spatial organization of the cytoskeleton in crayfish stretch receptor.

An electron microscopic study of the cytoskeleton of the crayfish stretch receptor was carried out. Longitudinal sections of the sensory neuron axons and dendrites showed wave-like arrays of microtubules with a period of about 5 microns. Transverse sections showed that the microtubules displayed no regularity in the arrays. In oblique sections, transverse and longitudinal views of microtubules (or shorter and longer segments of microtubules) alternated yielding a festoon-like pattern. The data obtained indicate that the cytoskeleton of the stretch receptor has a helical structure in which all the microtubules, the major cytoskeletal components, are arranged in parallel helices that are in register along the length of axons and dendrites. The helical organization of the cytoskeleton is probably responsible for the banded appearance of sensory axons and primary dendrites as seen in the polarized light. Decrease of contrast and disappearance of the banding during stretch of the receptor muscle are supposedly due to the desynchronization of the helical trajectories of the microtubules and to the decrease of the helical amplitude.

[Structural elements of z-disks]. / Strukturnye élementy z-diskov.

Structural features of the Z-line were examined in negative stained rabbit psoas myofibrils. The data obtained allow to conclude that: 1) the amount of overlap of actin-containing filaments from apposing sarcomeres is about 50 nm; 2) there are five bands of extra density separated by the distances approximately 20 nm across entire Z-line width, and three central of these bands are localized in the actin overlap region; 3) the axial repeating distance between Z-filament attachment sites on thin filament is found to be 17-20 nm. A model for the array of cross-bridges between action-containing filaments in Z-line is presented.

[Interaction of aldolase with thin filaments within I-disks, isolated from skeletal muscles]. / Vzaimodeistvie al'dolazy s tonkimi nitiami v sostave I-diskov, izolirovannykh iz skeletnykh myshts.

Using electron microscopy and optical diffraction, Ca2+-dependent binding of a glycolytic enzyme (aldolase) to thin filaments of isolated skeletal muscle I-disks have been revealed. On the micrographs of negatively stained I-disks the cross-striation determined by troponin-tropomyosin complex distribution has a period of about 38 nm. The width of troponin-tropomyosin stripes is 5-6 nm. On the optical diffraction patterns from isolated I-disks the meridional reflections measuring 38.5, 19.2, 12.8 nm are present. On the micrographs of isolated I-disks, treated with aldolase in the absence of Ca2+ (1 mM EGTA) the width of periodic transverse stripes (period approximately 38 nm) increases from 5-6 nm to 25-28 nm due to the interaction of aldolase with thin filaments. On the optical diffraction patterns from I-disks treated with aldolase in the absence of Ca2+ (1 mM EGTA) the strong meridional reflection equal to 38.5 nm is present, while the reflections equal to 19.2 nm are absent. The optical diffraction patterns from I-disks treated with aldolase in the presence of Ca2+ (greater than or equal to 10(-5) M) do not, as a rule, differ from those obtained from I-disks not treated with aldolase, i.e. they contain the three above reflections. The binding of aldolase to thin filaments in the absence of Ca2+ is the reason of disappearance of meridional reflections equal to 19.2 and 12.8 nm.

[Effect of temperature and pH on the environment of tryptophan residues in alpha-actinin]. / Vliianie temperatury i pH na okruzhenie ostatkov triptofana v alpha-aktinine.

Effects of temperature and pH on the structure of rabbit muscle alpha-actinin were studied by means of an intrinsic fluorescence method. Alkaline denaturation of alpha-actinin at 15 degrees C begins at pH above 9, while acidification of the solution does not cause unfolding of the protein structure, but results in protein aggregation. The maximal intensity of the isoelectric aggregation process is registered at pH 5. Thermal denaturation of alpha-actinin occurs within the temperature range from 45 degrees C to 65 degrees C. Protein has the second thermally induced transition in the region from 17 to 30 degrees C.

[Z-line structure of the rabbit psoas muscle studied by negative contrast staining]. / Issledovanie struktury Z-linii poiasnichnoi myshtsy krolika metodom negativnogo kontrastirovaniia.

The ultrastructure of the Z-disc of the rabbit psoas muscle was elucidated by electron microscopy using negative staining technique. Conclusions summarized from this work are as follow: (a) Z-disc involves two layers of Z-filaments, i.e. connecting filaments, which bind thin filaments of adjacent I-discs in the Z-line region. These layers are spaced about 380 A apart. (b) Z-filaments measure 380 A X 30 A. (c) The angle between the connecting filaments and the thin filaments depends on ionic conditions and varies from 20 degrees to 90 degrees. (d) We conclude that alpha-actinin is a structural component of Z-filaments, since dimensions of Z-filaments and their interaction with thin filaments are similar to those of alpha-actinin.

[Interaction of alpha-actinin and tropomyosin with F-actin]. / Vzaimodeistvie al'fa-aktinina i tropomiozina s F-aktinom.

The interaction of alpha-actinin, F-actin and tropomyosin has been investigated by using electron microscopy, SDS-gel electrophoresis and viscosimetry. It was shown that the temperature dependence of the interaction with F-actin was similar for alpha-actinins, isolated from the muscle of warmblooded animal (rabbit skeletal muscle) and from muscle of cold--blooded ones (cross striated part of the adductor of scallop Patinopecten yessoensis). The temperature rise from 0 degrees C to 37 degrees C results in a decrease of the affinity of alpha-actinin to F-actin. Tropomyosin decreases the amount of alpha-actinin bound to F-actin at 37 degrees C, but does not dislodge it completely from F-actin filaments. In this case the alpha-actinin binding also occurs along the entire length of the F-actin. It has also been shown that at 0 degrees C alpha-actinin and tropomyosin interact with F-actin independently of each other. The data obtained attest that tropomyosin and alpha-actinin have different binding sites on F-actin. The temperature and tropomyosin regulate only the amount of the bound alpha-actinin, but not its localization on the actin filament, as it was earlier supposed. These data allow one to conclude that the localization of alpha-actinin in Z-disk of cross-striated muscle can be determined neither by physiological temperature nor the presence of tropomyosin.

[Alpha-actinin of Primor'e scallop striated muscle. Physico-chemical properties]. / Alpha-aktinin poperechno polosatoi myshtsy primorskogo grebeshka. Fiziko-khimicheskie svoistva.

A protein with chain weight of about 90,000 Dalton (MP-90) was isolated from the cross-striated adductor muscle of the scallop Patinopecten yessoensis. The Physicochemical properties of MP-90 and its interaction with actin were studied in comparison with those of alpha-actinin of rabbit skeletal muscle. The data obtained allow us to conclude that this isolated protein is alpha-actinin of cross-striated adductor muscle of scallop Patinopecten yessoensis.